Thermal interrupter



Dec. 14, 1954 E. K. HODSON THERMAL INTERRUPTER Filed July 21, 1952 Fl GFl G 2 F I G 3 INVENTOR ERNEST K. HODSON,

ATTORNEY United States Patent THERMAL INTERRUPTER Ernest K. Hodson,Caldwell, Idaho, assiguor to Vernard Soper, Minneapolis, Minn.

Application July 21, 1952, Serial No. 300,004

7 Claims. (Cl. 200-122) This invention relates to a thermal interrupterof the thermal flasher type which is particularly adapted to control, inan intermittent manner, the supply of current or voltage to an electricfence whereby to energize such a fence. An interrupter, so used, isknown in the trade as a chopper and it is used to energize the fenceduring only a very short period and, thereafter, to de-energize thefence to permit an animal to withdraw from the fence after it has beenshocked.

It has been common practice in this art to employ a conventional type ofthermal flasher which is provided with the usual bimetal element that isdirectly heated by a heating coil. A normally closed contact between thebimetal and an adjacent terminal is broken when the current through thiscoil and closed contact permits the coil to heat up and to cause thebimetal to bend. In the event that such coil becomes open circuited asby a burnout or otherwise, the contact will become closed in a manner tosupply current continuously to the fence and that would be objectionablebecause an animal will very likely receive a prolonged shock.

According to the present invention, a novel and improved form ofinterrupter has been provided which comprises a primary bimetal elementand a secondary bimetal element. The primary bimetal element functionsas in a common form of thermal flasher to cause that bimetal to bend andbreak the heating coil circuit. The movement of this element, however,will not energize the fence transformer. The secondary bimetal elementis positioned adjacent to the primary element and coil in a manner toreceive heat from the single heating coil, associated with both of theseelements. This secondary element serves only to make and break theprimary circuit of the fence transformer and, when not heated, thissecondary bimetal functions to maintain this transformer deenergizedbecause this latter bimetal cooperates with the normally open contact.

The main object of the invention is to provide a novel form of thermalinterrupter that has a primary bimetal element and a secondary bimetalelement which unit has the usual normally closed contact associated withthe primary element and with an auxiliary or normally open contactassociated with the secondary element which latter bimetal element andcontact is in series circuit with the primary coil of the fencetransformer and which normally open contact functions, when open, tomaintain the transformer and fence deenergized whenever the heating coilbecomes ineffective to cause its associated bimetal to bend.

Another object is to provide a thermal interrupter that is compact inform and simple in structure and number of elements to the end that itcan be produced at a relatively low cost.

Other objects, aside from those that will appear from a study of thespecification, are to provide an interrupter that may be substituted forone of the common forms of flasher switches in use with an electricfence or that may be used to control any circuit in general that is tobe intermittently energized.

In the accompanying drawings:

Fig. 1 is a schematic wiring diagram showing the improved interrupter asembodied in a well known electric fence circuit.

gig. 2 is a view, in section, taken on line 22 of Fig. 3, an

Fig. 3 is a view. in section, taken on line 33 of Fig. 2.

Referring to Fig. 1, the stock enclosing fence 1 com- 2,697,152 PatentedDec. 14, 1954 prises, as usual, a single metallic bare wire. This wirebecomes energized when the primary coil P of the fence transformer isenergized since this wire is in series circuit with the transformersecondary coil S by way of conductor 2. When this wire is connected toterminal 4 of the impedance 3, the latter is not in circuit and a fullvoltage of from 2000 to 3000 volts exists between the wire 1 and theground. With this wire connected to terminal 5 of this impedance, theshock current would be materially reduced due to this series impedance.The coil S is grounded at 6 and an indicator lamp 7 is in this groundedcircuit to provide an operation signal.

An A. C. source 8' furnishes the energizing current to the coil P. Theimproved interrupter I comprises, in the main, a primary bimetal 9 and asecondary bimetal 3 secured to the bimetal 9 or mounted in a manner incontact therewith to readily receive heat from the heating coil 11either by heat conduction through contact with bimetal 9 or, to a lesserdegree, by heat radiated therefrom. Normally, when the main line switchSw is open, the contact of pair 12 is closed and the back contact ofpair 13 is open.

A conductor 14 connects one A. C. terminal with the lower one of contactpair 12 so that current may pass through bimetal 9 thence through coil11 connected as at 15 to the bimetal 9 and back to the other A. C.terminai. The upper contact of pair 13 is in series circuit with theprimary coil P by way of the conductor 16 and the return circuit isthrough the conductor 17 to the lower A. C. terminal, as shown. Anoperation signal 19, which may be a low wattage lamp or its equivalentis shunted across primary coil P in series with a resistance 20.

In normal operation, when the switch Sw is closed, a circuit isestablished through 14, 12, 9, 11 and 15 and the heating coil 11 willheat up. This will cause the bimet l 9 to flex upwardly to open contacts12. However, the bimetal 10 will remain cool for a short period or untilit becomes sufficiently heated by conduction from bimetal 9 and, inpart, by radiation from the coil 11. This coil will then start to cooloff as soon as contacts 12 open to permit this bimetal to flexbackwardly to reclose contacts 12. Only after several repeated openingand closing cycles of contacts 12 will the bimetal 8 become sufficientlyheated to cause it to flex upwardly to permit contacts 13 to close andthe latter will remain closed so long as the contacts 12 continue tocycle.

With the contacts 13 now closed, the primary coil P will becomeenergized intermittently each time that contacts 12 cycle and theenergizing current is by way of upper A. C. terminal, conductor 14,contacts 12, bimetal 9, through bimetal 8, through back contacts 13,conductor 16, coil P, conductor 17 and back to the lower A. C. terminal.

The constants of the interrupter elements are so designed as to causethe bimetal 9 to maintain the contacts 12 closed for only a shortperiod, say one second more or less. During this period, the transformersecondary S and fence wire 1 are energized and any animal in contactwith this wire will be in series circuit with this secondary through theground return 6.

Closure of contacts 12 causes coil 11 to heat up to again reopencontacts 12 whereupon the circuit through the primary P is broken withthe result that the fence wire is deenergized in a manner to permit theanimal to back away from this now dead wire after it has been shockedbut while it is no more under the influence of a shock current.

Considering the main object of the invention and its operationaladvantages, very often a heating coil asll will become defective. Itmight burn out to give an open circuit there hrou h or it mi ht becomegrounded onto the adjacent bimetal 9 in which latter case it would notprovide ample heat to cause bimetal 9 to flex upwardly. As a result, thecontacts 12 would remain closed and. as an undesired result, the fencewire 1 would remain energized if the interrupter embodies only thesingle bimetal now in common use.

However, if a defect as described should occur in this coil 11, it wouldcool off very ouickly and permit bimetal 9 of the interrupter shown inFig. 1 to also cool with the 3 advantageous result that bimetal 8 wouldalso cool off, flex downwardly to permit contacts 13 to open and remainopen. Hence the energizing circuit through the primary coil P wouldremain open and both signals 7 and 19 would indicate that the fence lineis not energized.

The secondary element 3 is designed to maintain contacts 13 closedduring cycling of the contacts 12 due to a higher heat retentivity ofelement 8 although the element 9 is permitted to flex downwardly againrelatively soon after the circuit of coil 11 has opened.

Figs. 2 and 3 show, in detail, the actual construction of a preferredform of the interrupter I of Fig. l. The elements thereof have beendesigned and corelated to provide an economical unit that may be readilyassembled, repaired and adjusted. An elongated headed rivet R is used toretain the elements of the unit assembled. The two bimetals 26 and 27and a pair of contact supporting bars 28 and 2% are spaced along thisrivet which passes through openings formed in the lower ends of thesefour elements. The bars are spaced from the rivet by means of aninsulating sleeve 34 and fibre washers 3. maintain the bars and theadjacent bimetals spaced from each, other. Terminal eyelets or lugs 32that contact the bars are soldered to a pair of short strong wires 33and 34 which, at their remote ends, are soldered to two of the prongs 35of the casing base 36. These wires support the entire interrupter unit.Metallic washers or rings 37 contact the bimetals 26 and 27 to connectsame electrically and to permit heat transfer between the same.

The normally open contacts 3838' are carried re spectively by the bar 29and the bimetal 27 and the normally closed contacts 39-39 are carriedrespectively by the bimetal 26 and the bar 28. The contact 39' is shownto be adjustable. The rivet R is peened over at 40, and against ametallic washer 41 in a manner to force 06 all elements on the rivettowards each other and the rivet head to maintain all elements rigidlyin position. A pair of fibre washers 42 serve to insulate lugs 32 fromthe rivet. The bimetal 26 is wound with a heating coil 43 that is spacedfrom the bimetal by insulation. The upper end of this coil is shown assoldered as at 44 to the bimetal 26 and its lower end 45 is soldered toa third prong 35 on the base 36. Hence, three of these prongs serve aslead in terminals to the contact 38, the contact 39 and to the coil 43and these connections correspond to the connections to the interrupter Iof Fig. l. The cycle of the device shown by Fig. 2 is the same as forthe interrupter shown by Fig. l. The following claims are made:

1. A thermal interrupter of the thermal flasher type comprising aprimary bimetal element and a secondary bimetal element, means to securesaid elements together at a corresponding pair of ends thereof in amanner to permit electrical and heat conduction between said elements, afirst contact positioned adjacent to the free end of the primary elementand normally closed into contact therewith, a second contact spaced fromthe free end of the secondary element but out of contact therewithnormally and prior to flexing of said latter element, a heating coil forheating the primary element and being operably responsive to closure ofthe first named contact, said elements being spaced from each otherexcept at the point where the elements are secured together, saidsecondary element being heated by its thermal contact with the primaryelement after the latter element has become heated and in a manner tocause the secondary element to flex towards said second contact to causeclosure of the secondary element against the second named contact apredetermined time after repeated closures of the circuit to theheatingcoil, with the result that, in the event the heating coil becomesdefective, said bimetal elements will cool and flex in a manner to causethe second contact to open and remain open.

2. A thermal interrupter comprising a primary bimetal element and asecondary bimetal element, means for holdmg corresponding ends of saidelements in electrical contact and m a manner to permit the secondaryelement to be heated by contact with the primary element, said holdmgmeans rigidly supporting said elements at their contacting ends topermit independent flexure of both elements, the free end of the primaryelement having an end contact, a second contact positioned to benormally closed against said end contact, a heating coil for saidprimary element, and having one end thereof connected to the latterelement electrically, the free end of the coil being connected to apower source conductor, a third contact on the free end of the secondaryelement, a fourth contact positioned adjacent the third contact and,normally, not in engagement therewith, whereby both elements are adaptedto flex due to heat from said coil to cause opening of the normallyclosed contacts and to cause closure of the normally open contacts saidsecondary element becoming flexed to close the third and fourth contactsa predetermined time after several repeated. closures of the first andsecond contacts with the result that, in the event the heating coilbecomes defective, said bimetal elements will cool and flex in a mannerto cause the third and fourth contacts to open and remain open.

3. In an interrupter as set forth in claim 2 wherein the normally closedcontacts are permitted to cycle to open and closed positions for alimited number of cycles to permit the secondary element to becomeheated by heat conduction from the primary element thereby to cause thenormally open contacts to permanently close whereby an energizingcircuit connected to the fourth contact will become closed through thenormally open contacts.

4. In an interrupter as set forth in claim 2 wherein, each successiveopening of the normally closed contacts will permit the primary elementto cool to a degree to cause reclosing of the normally closed contactsand a reenergization of the heating coil, in a series of repeatedcycles, during which cycling period the third and fourth normally opencontacts will remain closed due to the degree of heat retentivity of thesecondary bimetal element and which has become heated by conduction fromthe primary element across the supported contacting ends of the twoelements.

5. In an interrupter as set forth in claim 2, a base member, a series ofterminal prongs secured to the base, a pair of supporting bars, thesecond and fourth contacts being carried respectively by said bars,means to position the primary and secondary elements between said bars,and a lead wire connecting each supporting bar to a respective prong andserving to support the bars and elements upon said base.

6. In a thermal interrupter, a base member, a series of terminal prongscarried thereby, an elongated metallic supporting member, a primarybimetal element and a secondary bimetal element supported by said.member at corresponding ends of the elements, means to connect said endstogether in a manner to permit electrical and heat conduction betweenthe elements, an insulating sleeve for spacing the elements from saidmember, a contact on the free end of each element, a contact normallyclosed against the primary element contact and another contact normallyopen with respect to the contact on the end of the secondary element, aheating coil associated with the primary element and serving to heat thelatter element to cause opening of the normally closed contacts, saidsecondary element being, in turn, heated by conduction of heat from theprimary element.

7. In an interrupter as set forth in claim 2, apair of power supplyconductors, one conductor being connected to the second named contactand the other conductor being connected to the free end of the heatingcoil to cause ieating of that coil, and a circuit to be energizedintermittently, one end of said circuit being connected to the fourthcontact and the other end of the circuit being connected to said otherconductor.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,428,525 Osterheld Oct. 7, 1947 2,574,869 Green Nov. 13, 19512,623,137 Vogelsberg Dec. 23, 1952

